1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image on a photosensitive recording medium and, more particularly, to an image forming apparatus capable of forming an image of high quality even in a highly humid atmosphere.
2. Description of Related Art
A conventional image forming apparatus using a photosensitive recording medium, such as a photosensitive pressure-sensitive recording paper, exposes the photosensitive recording medium to light in an atmosphere having a fixed temperature because the sensitivity of the photosensitive recording medium is dependent on temperature. The exposed photosensitive recording medium is then subjected to a pressure-fixing process for a heat-fixing process. It is possible for the photosensitive layer to fall off in the pressure-fixing process under a highly humid condition.
A photosensitive pressure-sensitive recording paper can include, for example, numerous light-setting microcapsules containing a dye which reacts with a developer to develope color, bound to a base paper with a water-soluble binder. When this photosensitive pressure-sensitive recording paper is irradiated by light reflected from an original to form a latent image, the microcapsules exposed to light harden and the unexposed microcapsules remain unhardened. The photosensitive pressure-sensitive paper carrying the latent image and a developing paper are superposed and a high pressure is then applied to both sides of the superposed photosensitive pressure-sensitive recording paper and the developing paper to crush the unhardened microcapsules. Consequently, the dye and the developer interact to develop an image on the developing paper.
The binding effect of the binder will be reduced when the binder absorbs moisture from a highly humid atmosphere and a photosensitive layer consisting of the binder and the microcapsules is liable to separate from the base paper. Consequently, portions of the binder and microcapsules are undesirably transferred to the developing paper which deteriorates the quality of the image formed on the developing paper. Such a problem may be solved by additionally providing the image forming apparatus with a dehumidifier or the like to reduce the absolute humidity within the image forming apparatus, however, this requires an increase in the size of the image forming apparatus.
In U.S. patent application Ser. No. 167,198 (filed Mar. 11, 1988) assigned to the same assignee of the present application, there has been proposed a method of reducing the relative humidity within the image forming apparatus by raising the temperature of the photosensitive medium or that of the ambient atmosphere. However, since the sensitivity of the photosensitive medium is dependent on temperature, raising the temperature may change the photosensitive characteristics of the photosensitive medium and deteriorate the quality of the image.